Riverview, Florida -- Firefighters say the daughter of a man killed in his burning house early Friday morning lives right next door, but wasn't able to help him.

At 3 a.m. Friday, firefighters were called to Cone Grove Road in Riverview. As they arrived, Hillsborough County Fire Rescue crews could tell the fire had been burning and growing for some time before it was reported.

Firefighters had the flames down and out in 20 or 25 minutes, a spokesman said. As they fought the flames, firefighters in their heavy "bunker gear" pressed into the house, searching in the heat and smoke for anyone inside.

That initial sweep found no one.

Then, fire crews talked with the daughter of the elderly man who lived in the house. The daughter lives right next door.

"She stated that her dad possibly was in the home. She was not sure at the time," said HCFR spokesman Ronnie Rivera. "That's when our crews heard the news and we started searching right away for possible victims."

That secondary search found the woman's father in a bedroom. He had not survived.

Fire investigators expect to be inside the charred shell of the house for several hours Friday morning.

They're working to uncover what started the fire and determine why the man wasn't able to escape the fire.

Rivera admits the investigation will be challenging because of the severe damage, which collapsed the roof of the garage and charred and gutted a large part of the home.